Many rotary offset printing machines have serially arranged printing stations in which sheets from a first printing station are transferred to a storage drum and then over another drum to a second serially arranged printing station. The other drum can be so arranged that the sheet is transferred either in its normal course of movement, or turned end-for-end, so that a previously printed page will always be uppermost, or respectively inverted with respect to the drum. Such a drum is referred to as a reversal drum since, selectively, the sheet can be transferred straight or reversed. This is obtained by gripping either the forward edge of the sheet being transferred, or the rearward edge, so that the sheet on the reversal drum will then continue to be fed in either upward or turned-over position.
Sheet reversal devices of this type have been described in the literature see, for example, U.S. Pat. No. 3,796,154, Weisgerber, to which German Patent Document DE-AS 2,133,693 corresponds. The overall arrangement then permits single-sided printing in multiple colors by the serially arranged printing stations, or serial printing on both sides of the sheet.
Sheet reversal apparatus of the known type are so arranged that the storage drum has double the diameter of the plate cylinders of the printing stations so that, upon reversal, the storage drum can accept printed sheets having a format which exceeds the printed space defined by the geometric arrangement of the transfer drum. The increased diameter of the storage drum not only requires additional space in the printing machine and, since the storage drum will require two sheet gripper systems, substantial additional costs in manufacture and eventual maintenance, but additionally requires extremely accurate sheet feeding to prevent differences in match and alignment of the sheet with respect to the serially arranged printing stations, since the printed sheet must be transported over two different sheet gripping systems.